1) Field of the Invention
The present invention generally relates to a switch which is surface-mountable on a circuit board and, more particularly, to a surface-mountable switch having an opening sealed with a tape seal to prevent invasion of a cleaning liquid into an inner space when the switch is subjected to a cleaning process and a manufacturing method of such a switch.
A small switch is mounted on a circuit board provided in electronic equipment such as a computer so as to switch an operational mode of the electronic equipment. Such a switch is surface-mounted on the circuit board. A switch knob for operating the switch is normally exposed outside from an opening formed on a top surface of the switch.
The switch is soldered onto the circuit board together with other electronic parts such as semiconductor devices by means of a solder reflowing process. The circuit board is subjected to a cleaning process after the reflowing process so as to remove a flux adhering on the circuit board. Since the semiconductor devices are completely sealed by a plastic molding, the semiconductor devices are not affected by the cleaning liquid when the circuit board is dipped into the cleaning liquid. However, since the above-mentioned switch has the opening for the switch knob, the cleaning liquid may invade into an inner space of the switch through the opening. If the cleaning liquid enters inside the switch, it may cause a corrosion of materials inside the switch and result in a bad electrical contact of the switch. Accordingly, in order to prevent the invasion of the cleaning liquid when the cleaning liquid is splashed on the switch, a tape seal is provided to cover the opening formed in the switch.
2) Description of the Related Art
FIGS. 1A and 1B show a small slide switch 1 (hereinafter referred to as a switch 1) which is surface-mounted on a circuit board of an electronic equipment. The switch 1 comprises a switch body 4 which includes a lower base 2 and an upper cap 3. A switch knob 5 is slidably provided inside the switch body 4. Leads 6 and 7 made of an electrically conductive material are provided on the lower base 2. Brushes 8a and 8b made of an electrically conductive material are attached on a bottom surface of the switch knob 5. The brushes 8a and 8b are electrically connected to each other.
An operational part 5a formed on a top surface of the switch knob 5 is exposed to the outside from an opening 9 formed in the upper cap 3. When the switch knob 5 is moved in directions indicated by arrows A1 and A2 in FIG. 1B via the operational part 5a, the switch knob 5 slides in the switch body 4. Accordingly, the brushes 8a and 8b attached on the switch knob 5 are moved to electrically connect or disconnect the leads 6 and 7.
Since the switch 1 is to be surface-mounted on a circuit board with other electronic parts, the leads 6 and 7 together are formed in a gull-wing shape. The switch 1 is mounted by means of a solder reflowing process, and thus a flux remaining on the circuit board must be removed, after the reflowing process, by a cleaning treatment which uses a cleaning liquid. Since the switch 1 has the opening 9 for the switch knob 5, the cleaning liquid may enter inside the switch body 4 if no measures is taken.
In order to prevent the invasion of the cleaning liquid into the switch body 4, a tape seal 10 is applied on a top surface of the switch 1 so as to cover the opening 9 as shown in FIG. 2. Conventionally, the tape seal 10 adheres onto the top surface of the switch body 4 by a thermal curing type adhesive 11. The adhesive 11 is applied on the top surface of the switch body 4 beforehand, and then the tape seal 10 is put on the top surface of the switch body 4 with the adhesive 11 therebetween under atmospheric pressure. The adhesive 11 is cured by applying heat to secure the adhesion of the tape seal 10 to the switch body 4.
The above-mentioned process for applying the tape seal 10 is performed at an end of a manufacturing process of the switch 1. Accordingly, the switch 1 is soldered onto the circuit board in a state where the tape seal 10 is applied.
In a state in which the opening 9 is covered by the tape seal, an inner space 12 (refer to FIG. 2) formed between the lower base 2 and the upper cap 3 is hermetically sealed. Accordingly, when the switch 1 is heated in a heating process for soldering, air in the inner space 12 is expanded by heat. Accordingly, air pressure in the inner space 12 is increased, and thereby the tape seal 10 is pressed from inside by the thermal expansion of the air. This may cause, in a worst case, a breakage of adhesion of the tape seal 10 as shown in FIG. 3 which release the air confined in the inner space 12. This results in an incomplete seal of the opening 9 due to an opening or a hole formed between the tape seal 10 and the top surface of the switch body 4. It should be noted that FIG. 3 shows the switch 1 mounted on a circuit board 14 by a solder 15 applied to the end of each of the leads 7 and 8.
When there is formed the above-mentioned opening or hole, there is a problem in that the cleaning liquid enters into the inner space 12 during the cleaning process, and thus a bad electrical contact and a corrosion of materials in the inner space 12 occur.